This invention relates to an ink-jet printable transfer material having a heat-activatable adhesive layer.
Transfer materials have been available for many years and serve the decoration of goods. Typically they consist of a polymeric or wax film which is formed on a support. An image is printed on the film and subsequently the film is transferred from the support to a substrate usually by applying pressure or heat to the back of the support.
FR 2 715 607 B1 describes a method for decorating a substrate with an image which, at first, has been printed on a transfer material. A digital image from a conventional video camera is printed using an ink-jet printer onto the transfer material which comprises a plastic support and a heat sensitive adhesive coating onto which the ink is printed. The printed side of the transfer material is placed in contact with the substrate and heat is applied to activate the support. The plastic support can be removed once the adhesion between the coating and the substrate is greater than that between the coating and the plastic support. FR 2 715 607 does not disclose the composition of the coating which accepts the printing ink. However, non-heat-sealable coatings are essentially continuous films deposited from a polymer solution in an organic solvent or water, or from a dispersion of a polymer in water with emulsifiers.
WO 98/35840 describes a transfer film for transferring an ink comprising at least one liquid component, the film comprising a porous matrix of particles of a heat activatable adhesive bound together by an absorber, the absorber being at least partly soluble in the said liquid component within the porous matrix, and the absorber preferably being within the pores of the porous matrix. The absorber has the double function of binding the matrix of heat activatable adhesive and at least partially absorbing the liquid component of the ink.
The absorber is a water soluble or hydrophilic absorber, i.e. an acrylate copolymer, a cellulose ether and/or a polyvinyl pyrrolidone. However, the printed image on the transfer material of WO 98/35840 shows a grainy performance.
It is therefore an object of this invention to provide an improved image transfer material which does not show the above-mentioned disadvantages. The improved printable transfer material shall provide high color densities, even image quality, short drying time and, in particular, good adhesion on the permanent carrier.
This object is achieved by a printable transfer material comprising a support and a heat-activatable polymer layer wherein the polymer of that polymer layer is a mixture of nonionic water-soluble poly(ethyleneoxide)polymers with the general formula
Hxe2x80x94[xe2x80x94Oxe2x80x94CH2xe2x80x94CH2xe2x80x94]nOH,
wherein the degree of polymerization n is in the range of from 1,000 to 200,000, in particular, from about 2,000 to 180,000.
It was found that the polymer used in the present invention can serve the dual function of an absorber for the ink and as a heat activatable adhesive. It is assumed that this fact has a profound effect on the print quality of the image. The coating comprising that polymer is applied in the form of a homogeneous solution of single polymers, whereas the transfer film of WO 98/35840 is obtained by applying a non-homogenous dispersion of two non-miscible polymers. In the prior art document only the absorber polymers are capable of absorbing the ink and the colorant, while the heat-activatable adhesive will not.
The transfer material of the invention results in an improved image quality and improved optical density of the print.
Although not necessary for the purpose of the present invention, the polymer layer may contain additional polymers. The polymer layer may contain pigments such as silica, alumina, aluminum hydroxide, calcium and/or magnesium containing compounds. By the presence of these or other pigments known in the art the ink absorption may be improved and bleed of the ink is avoided or at least decreased. The ratio of the polyethylene oxide to the pigment is from 20:1 to 1:1, preferably from 15:1 to 5:1, based on the weight of the components.
The polymer layer may contain dye fixing agents such as quaternary polyammonium salts, cationic polyamines, cationic polyacryl amides or cationic polyethylene amides. Particularly preferred are polyquaternary amines. The amount of the dye fixing agent should not exceed 5% by weight, based on the weight of the dry layer. Preferably, the amount of the dye fixing agent is in the range of 0.1 to 3.0% by weight, based on the dry weight of the layer.
The polymer layer may contain additional additives such as wetting agents, dispersing agents or colorants.
Suited as a support are resin coated papers or plastic films. The thickness of the support generally is 1 to 500 xcexcm, preferably 5 to 200 xcexcm. Examples for resin coated papers include papers which are coated with polyolefins or polyesters. Suitable plastic films for the purposes of the present invention include, for example, polyester films or polypropylene films. Additionally, films made of polycarbonates, polyamides, polystyrene, cellulosic esters and metals are suited for the purposes of the present invention.